Hi all: As the primary Colorado eBird reviewer, I have noted a wide variety of tacks that eBirders have taken when entering this late ibis in their eBird checklists. Many have entered it as a White-faced Ibis, using the rationale of that species being, by far, the most-common of the two dark ibis species that occur in Colorado. Others have entered it as a Glossy Ibis on the strength of the bird's dark (not red) eyes. Unfortunately, there are problems with both of these tacks.
The bird that has been present at Walden Ponds for a bit and which has been photographed many times is a juvenile/immature. As with many species of birds, accurate ageing of individuals is critical to accurate identification of said. As David Sibley states for BOTH species in the latest edition of his guide, "Immature may be indistinguishable from" the other species. I think that he's far too liberal. As far as I know, there is no certain way to field-ID juveniles of Glossy and White-faced Ibises. Both species sport dark eyes as juveniles and young immatures, with the eye color of young White-faceds not beginning to change to red until late fall, at the earliest, with Sibley stating "iris red by Feb." The more-important aspect of this missive, however, is that just because White-faced Ibis is, overall, the "expected" species of Plegadis in Colorado, does not at all mean that any particular individual can be identified as such on that criterion alone. There are way too many records of Glossy Ibis spread across the state for ID by range map in this genus to be certain; every individual reported to species really should be IDENTIFIED as such in the field, not assumed to be a White-faced. Further, and much more problematic, is that a large number of Plegadis hybrids have been found and identified in Colorado, and these can look like either parental species or something in between (see http://cobirds.org/CFO/ColoradoBirds/InTheScope/32.pdf). It has been shown time and again, that immatures of species are the ones most likely to wind up finding themselves outside of typical range of the relevant species. Also, temporally atypical occurrences of individuals of east-west species pairs have also been shown often to be referable to the rare local species of a group. For example, Ash-throated Flycatcher is far-and-away more likely on the East Coast north of Florida in November than is Great Crested Flycatcher, which is the local breeder Ash-throated -- http://ebird.org/ebird/map/astfly?neg=true&env.minX=146.17967353256398&env.minY=-2.6167331691492874&env.maxX=26.29686103256404&env.maxY=68.08042679267473&zh=true&gp=false&ev=Z&mr=on&bmo=11&emo=11&yr=all&byr=1900&eyr=2015 Great Crested -- http://ebird.org/ebird/map/grcfly?neg=true&env.minX=-88.75196709243596&env.minY=34.5584734059442&env.maxX=-58.73731865493596&env.maxY=43.8958046887706&zh=true&gp=true&ev=Z&mr=on&bmo=11&emo=11&yr=all&byr=1900&eyr=2015 So, all of the above verbiage has been spent in hopes that observers of the Walden Ponds ibis use the "Glossy/White-faced Ibis" category rather than either of the two species categories, as the bird cannot be specifically identified at this time. I also STRONGLY encourage the use of this category during all seasons when individual ibis (or flocks of ibis) are not or cannot be definitively identified to species. Thanks, Tony Leukering currently Cut Bank, MT -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/1509d282869-de6-6550%40webstg-m08.mail.aol.com. For more options, visit https://groups.google.com/d/optout.
